error[E0207]: the type parameter `C` is not constrained by the impl trait, self type, or predicates
  --> $DIR/unconstrained-param-ice-137308.rs:13:6
   |
LL | impl<C: ?Sized> A for u8 {
   |      ^ unconstrained type parameter

error: the type has an unknown layout
  --> $DIR/unconstrained-param-ice-137308.rs:18:1
   |
LL | struct S([u8; <u8 as A>::B]);
   | ^^^^^^^^

error: aborting due to 2 previous errors

For more information about this error, try `rustc --explain E0207`.